Hey,
On Tue, May 19, 2015 at 05:54:54AM -0400, Frediano Ziglio wrote:
> This problem happens using KMS surfaces and QXL driver.
> To easy reproduce use KDE Plasma (which use surfaces a lot) and assure
> you are using KMS surfaces (QXL driver on Fedora/RedHat has a patch to
> stop using them). Open some complex application like LibreOffice and
> after a while your machine get stuck using 100% CPU on Xorg.
> The problem occurs as creating new surfaces not interruptible wait
> are used however instead of returning ERESTARTSYS back to userspace
> you try to loop but wait routines always keep returning ERESTARTSYS
> once the signal is marked.
> On out of memory conditions TTM module try to move objects to system
> memory and QXL assure surface is updated before the move.
> The fix handle differently this case using no interruptible wait so
> wait functions will wait instead of returning ERESTARTSYS.
> Note the when the loop occurs driver will send a lot of update requests
> causing more CPU usage on Qemu side too.
>
> Signed-off-by: Frediano Ziglio <fziglio at redhat.com>
> ---
> qxl/qxl_cmd.c | 12 +++---------
> qxl/qxl_drv.h | 2 +-
> qxl/qxl_ioctl.c | 2 +-
> 3 files changed, 5 insertions(+), 11 deletions(-)
>
> diff --git a/drivers/gpu/drm/drivers/gpu/drm/qxl/qxl_cmd.c b/qxl/qxl_cmd.c
> index 9782364..bd5404e 100644
> --- a/drivers/gpu/drm/qxl/qxl_cmd.c
> +++ b/drivers/gpu/drm/qxl/qxl_cmd.c
> @@ -317,14 +317,11 @@ static void wait_for_io_cmd(struct qxl_device *qdev,
> uint8_t val, long port)
> {
> int ret;
>
> -restart:
> ret = wait_for_io_cmd_user(qdev, val, port, false);
> - if (ret == -ERESTARTSYS)
> - goto restart;
I think this one is not directly related to the fix, but can be removed
because wait_for_io_cmd_user(qdev, val, port, false); will call
wait_event_timeout() which cannot return ERESTARTSYS? Or was this loop
causing issues too?
> }
>
> int qxl_io_update_area(struct qxl_device *qdev, struct qxl_bo *surf,
> - const struct qxl_rect *area)
> + const struct qxl_rect *area, bool intr)
> {
> int surface_id;
> uint32_t surface_width, surface_height;
> @@ -350,7 +347,7 @@ int qxl_io_update_area(struct qxl_device *qdev, struct
> qxl_bo *surf,
> mutex_lock(&qdev->update_area_mutex);
> qdev->ram_header->update_area = *area;
> qdev->ram_header->update_surface = surface_id;
> - ret = wait_for_io_cmd_user(qdev, 0, QXL_IO_UPDATE_AREA_ASYNC, true);
> + ret = wait_for_io_cmd_user(qdev, 0, QXL_IO_UPDATE_AREA_ASYNC, intr);
> mutex_unlock(&qdev->update_area_mutex);
> return ret;
> }
> @@ -588,10 +585,7 @@ int qxl_update_surface(struct qxl_device *qdev, struct
> qxl_bo *surf)
> rect.right = surf->surf.width;
> rect.top = 0;
> rect.bottom = surf->surf.height;
> -retry:
> - ret = qxl_io_update_area(qdev, surf, &rect);
> - if (ret == -ERESTARTSYS)
> - goto retry;
> + ret = qxl_io_update_area(qdev, surf, &rect, false);
My understanding is that the fix is this hunk? If so, this could be made
more obvious with an intermediate commit adding the 'bool intr' arg to
qxl_io_update_area and only calling it with 'true' in the appropriate
places.
This code path is only triggered from qxl_surface_evict() which I assume
is not necessarily easily interruptible, so this change makes sense to
me. However it would be much better to get a review from Dave Airlie ;)
Christophe
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